Re: equal length pitman and idler arms, this is what I based my earlier statement on:
http://www.freeasestudyguides.com/id...g-linkage.html.
Yet, I recall my 1st ps-conversion, on a 1966--years ago. I adapted a later (unknown year) ps box w/its pitman, using spacers, and bolted it to the frame
'wherever the box wanted to go' after attaching the box/pitman to the factory '66 center link. After hanging first bolt, I
did eyeball the clearance between x-member and drag link before drilling next hole. But, I did absolutely nothing to the stock idler arm--still not knowing today how near to same length the idler was to pitman. I'd agree to beginner's luck if someone accused me of that!
If all else seems to fail, the box may be mounted too close to the firewall.
I, too, send a good luck to your endeavor.
Sam